In the field of communications, the need for high-speed transmission of data, including video and audio, has continued to increase. Moreover, there has been an increase in the selection of services by which users can connect to a network, such as the Internet. Specifically, Internet Service Providers (ISPs) may allow for connectivity to the Internet through lower-speed connections at different rates, such as 56 kilobits/second, by employing a Plain Old Telephone Service (POTS) line. Other choices for connection, which are at higher speeds, into a network can include Integrated Services Digital Network (ISDN), Digital Subscriber Line (DSL) service, and cable modem service over a Radio Frequency (RF) cable line. Further, other types of content providers may enable a subscriber to receive different types of media, such as a video stream, audio stream, etc.
In a typical DSL network, a network element supports a wide variety of features to facilitate the management, allocation and distribution of IP addresses. Normally, the subscriber profile can be configured locally on the network element or can be retrieved from a RADIUS (remote access dial in user server) remote server (e.g.). A subscriber profile determines how an IP address (and optionally the associated route for the subscriber LAN) would be provided to a certain subscriber.
Typically, a DHCP (dynamic host configuration protocol) server is responsible for allocating and assigning one or more IP addresses to one or more clients. FIG. 1 is a block diagram illustrating a typical network configuration. In this configuration, a network element 101 serves a relay agent with respect to DHCP server 102 for one or more clients 103 and 104. Typically, when client 103 desires to enter the network, client 103 sends a DHCP discovery broadcasts to network element 101. Network element 101 forwards the request to DHCP server 102. DHCP server 102 then returns an offer back to network element 101 which in turn forwards it back to client 103. When DHCP 102 assigns an IP address to client 103, DHCP 102 replies with a DHCP packet (e.g., a DHCPack) to client 103. When network element 101 forwards this DHCP reply to client 103, network element 101 installs an IP-host route and an ARP entry for the IP address assigned to client 103. Client 103 now has a valid IP address and it knows the IP address of the DHCP 102. Further communications between client 103 and DHCP 102, such as DHCP lease renewal and release, will take place between client 103 and DHCP 102 directly without substantially invoking network element 101.
However, since network element 101 may communicate and service thousands of clients. Each client may need to directly communicate with DHCP 102 for, for example, IP address renewal or release. DHCP 102 may also service other network elements, which may provide services for thousands of other clients. As a result, DHCP 102 may experience heavy traffic from all clients via all network elements.
An IP address may be explicitly released by the client or implicitly released through the expiration of the lease time. In either case, sub-released IP addresses should be available for allocation and assignment.
When client 103 releases the IP address back to DHCP 102, network element 101 has no knowledge whether the IP address has been released until network element 101 sees DHCP 102 assigns that IP address to another of network element's 101 clients. Instead, network element 101 keeps listening to the traffic associated with the IP address until network element 101 sees DHCP 102 assigns that IP address to another of network element's 101 clients. Thus, network element 101 may consider that the IP address is still in use even though client 103 has released the IP address (directly back to DHCP 102). In addition to the resources of network element 103 wasted on such listening, this approach may result in an under utilization of IP addresses where DHCP 102 is serially resulting the network elements. Specifically, where DHCP 102 is servicing multiple network elements, DHCP 102 cannot allocate and assign a released IP address to a first network element while a second network element is listening for that IP address (that is, since the second network element listening for the released IP address will not see the reallocation and assignment of that IP address to a client of the first network element. The second network element will not know to stop listening and problems arise if two network elements are listening for the same IP address). This restriction typically leads DHCP 102 to be configured to designate different blocks of IP address to different network elements; if a given network element needs additional IP addresses, DHCP 102 cannot give it IP addresses designated to another network element even if they are not being used.
In addition, DHCP 102 typically maintains all lease time information for all clients. As a result, every client's DHCP renewal or release has to be processed by DHCP 102, which significantly increases the overhead traffic of DHCP 102. Furthermore, since network element 101 has no knowledge when the lease time expires, network element 101 has to keep listening for the IP address associated with the expired lease. Since allowing a lease to expire has the same effect as a client explicitly releasing an IP address, listening to an IP address for which the lease has expired has the same disadvantages as those described above with regard to when a client explicitly releases an IP address.